Suggestions for muscle car sound muffler without drone

I see the website to calculate tube length and show you all the harmonics is not valid anymore. So here's the equation
Frequency (f) = Velocity of Sound (V) / WaveLength (Lw). Assume a working resonator temp of 50 degrees C (122 F): V is 1187 Ft/sec. So knowing the frequency and velocity of sound you can calculate wavelength. Wavelength divided by 4 will give the quarter wavelength for your pipe length.